The central theme of this intervention development study is that regular exercise should be an adjunct therapy for older women to reduce the incidence of hip fracture. One out of every three white women 85 years and older are likely to experience a hip fracture, which leads to a loss of independence and a lower functional capacity. The primary approach for hip fracture prevention has been replacement estrogen. The long- range goal of implementing exercise as an adjunct therapy is to extend the time of first hip fracture by 5-10 years, resulting in a potential 30-50% reduction in hip fracture. The purpose of this intervention development study is to study the effects of participation in a three- year home-based exercise regimen for 105 women 65-78 years of age on risk factors related to bone and falling. An unique aspect of this study is that the volunteers will be long-term users of estrogen replacement therapy who have femoral neck bone mass >1 SD below the young adult level. The primary hypothesis to be tested is that women aged 65-78 years who are current users of estrogen replacement therapy and have low femoral neck bone mineral density will maintain sufficient compliance and retention in a 3 year home-based aerobic exercise and resistance training program to reduce risk factors regarding bone quantity and quality for osteoporosis, and falls. The specific aims to test this hypothesis are: 1) To evaluate the effectiveness of 3 year home-based exercise intervention on bone mass and geometric properties of the proximal femur. 2) To evaluate the effectiveness of home-based exercise intervention to improve formation relative to resorption, as evaluated by biochemical markers of bone metabolism. 3) To evaluate the effectiveness of home-based exercise intervention on risk factors for falls (balance, muscular strength and endurance, gait, lean body mass). A multivariate repeated measures factorial analyses of variance will be done to determine changes in the outcome measures as influenced by the determinants of bone mass. This proposal will establish an exercise regimen that may be implemented as an adjunct therapy to estrogen in older women to preserve or improve bone strength to delay the onset of first hip fracture.